Non-darkening lithophone and process of making the same.



' ciully.

UNITED sT tpEs PATENT OFFICE.

IENS P. LIHME, OF CLEVELAND, OHIO, ASSIGNOR TO GRASSELLI CHEMICAL COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF OHIO.

NON-DABKENING LITHOPCNE AND PROCESS OF MAKING TIDE SAME.

Specification of Letters Patent.

Potented March 24-, 1908.

Application filed. December 11, 1905. Serial No. 291,226.

To all whom it may concern:

Be it known that I, Inns P. lilHME, a citizen of the United States of America, and a resident of Cleveland, in the county of Guyahogs and State of Ohio, have invented certain new and usefui Improvements in Non- Dsrkening Lithopones and Processes of Multing the Same, of which the foliowing is a specification.

My invention relates to improvements in a non dai'keuing litliopone and process of making the some, and has for its ob'cctthe pro duction of s lithopone, wh Wil i not change color or he reduced undciconditions of exposure to suniight and moisture. All lithopones now on the morlict contain impurities, which, as I believe, are reduced under the foregoing named conditions und deposit inc tailic zinc in minute quuutit as, thus giving the pigment a slaty gray or darhcne tint. In consequence, lithoponc, although well adapted for use in the pointing trade, is undesirable for use a body for inunufucturing white-paints, and l have sought to ovoid this pmcticull prohibitive feature.

In my prior application, Ser. No, 289,238,

filed lio'vemher 27th, 1905, I hove explained my discovery an'fd theory more in detail and one method of overcoming the above re ferred to tendency of lithoponc to reduce. Herein I shall explain unothci" mode of producing a, non-darkening lithopone, which i have found desirable to practice commcr 'llici'n'cticully, lithoponcis u mixture comprising one molecular Weight of barium sulfate and one of zinc sulfid, but as monufcctured commercially, various impurities necessarily are present and must hc dcalt with, if harmful to the completed product. Solutions of the two precipitating salts; burium suh'id and zinc sulfate, are made up to contain known weights thereof. In the latter solution, discolor-mg impurities, which :n'e principally iron and manganese in combination, will almost inevitably be found, which arc precipitated out by chlorination This introduces u small uniount of zinc chlorid, while the barium -.olulion'contains such illlPUIltlCS as hydroxid, suliitc and l1yposullitc. Those two commercial solutions are mixed together, a small percentage of sodium chlorid preferably bcing previously added to the zinc sulfutc'in order to make the insulting precipitate more flocculcnt. The thcoreticsil reaction is as follows:

13218 I Z1180, B5150, ZnS.

so, soon 2 Biso, up.

In addition to this, the very high tompem ture in the mufl'lc necessarily d'ecomposcs some of the ammonium chlorid into hydro} chioric acid and ammonium gas; the hydro-- (-hloric acid acting upon the zinc oxid, and this in turn, at the high temperature, is con Wort-ed intd basic zinc chloiid;-Zn(7l,CZinG) which is demonstmtcd to be pmsenhsinoeit insoluble in tutor. The show, ihe have, indicate the reactions which icon the objecti "iable impurities in the lithopone.

it i 1y host judgmcnt, based upon at long series experiments, that it is the barium. E-f-Uli'lll(, hen brought into cou'ibinntion with 7 the basic zinc vhlorid, which the darkening of lillwponc; thc first under the inilucn'cc ol' the sun and in the presence of moisture, pmhabl beiu" first reduced to the form of bi-mdlitc, mid t his reacting on the basic zinc chloi'id canvases the reduction of the metallic 2h probably in ziccoi'duncc with this iornuii...

BuHJS-UQ F ZnFlfiZuQ:

BaSO -l- ZnSU ZnCl,,+ 2Zn H O. My experiments have shown that a neutral mixture of litho one and water gives an acid reaction, when t 1e change of color takes pIla-ce in the presence; of strong sunlight. aving ascertained what up ears to be the true cause of this undesira le Tcuction, I have sought to provide simple means for prc venting its occurrence in the completed prod- 9% see uct. Accordingly, I add to the lithopone at any suitable stage during the nrocess a salt or reagent, which will prevent t -e occurrence of undesirable reactions, causing a darkening of the lithopone.

After the product has been removed from the muffie and dum edinto vats of water to wash out any solub e impurities, I may add the reagent in sufiicient quantities, corresponding to the amount of undesirable imurities present, during the ensuing process of filtration. To obviate the darkening reaction, accordingly, I add to my lithopone, immediately before the last filtration, a small amount of caustic soda and a varying amount of nitrate of ammonium, or of other suitable nitrates or oxidizing agents. This will leave with the completed lithopone a suf ficient amount of such oxidizing agent, as to obviate any tendency of the zinc comthe preferred oxidizing agent in the form of a solution, the amount being dependent upon the volume of undesirable impurities, it will be apparent that a very finely pulverized nitrate or other oxidising agent may be added in a dry state during the latter steps of the process ofpreparing the litho one in its commercial form. Accordingly,, do not desire to be understood as restricting my invention to the precise ste )s above outlined, nor do I intend to assert that there may not be other causes for the darkening of the litho- ,pone, but my resent invention seeks to obviate this ten ency by adding a suitable reagent to prevent the occurrence of reactions in the com leted article, when exposed to sunlight ant moisture.

Having now set forth a process for manufacturing a non-darkening and highly purified commercial lithopone, I claim as new and desire to secure by Letters Patent, the following 1. The rocess of manufacturing a nondarkening ithopone, which consists 111 adding to the lithopone a soluble nitrate for preventin reaction among the impurities present, substantially as set forth.

The process of manufacturing'a nondarkcning lithopoue, which consists in preparing in solution commercial barium sulfid and zinc sulfate, purifying and mixing the solutions, mutiiing the product and adding thereto a soluble nitrate for preventing re action among the impurities, substantially as set forth.

3. A commercial lithopone, com )rising a mixture of barium sulfate, zinc sul 1d and a soluble nitrate; the latter being present in quantities corresponding to the reacting or darkening impurities, substantially as set forth.

Signed at Cleveland, this ninth day of December, 1905, in the presence of two subscribing witnesses.

'FRANOIS H. ECKHARDT,

G. E. Frsnnn. 

